The present invention is directed to overcoming problems associated with securing a lath to a sheathing (or a wall structure). In wall construction, plaster is generally applied to a flexible lath material instead of directly attaching the lath to a rigid structure, such as sheathing, because the current means of attaching a lath directly to a rigid structure can cause cracks. By applying plaster to a metal lath (which include structures such as welded wire, woven wire, and expanded metal lath), the plaster cracks less frequently than if compared to applying the plaster directly to the sheathing. The current method of fastening laths to sheathing is either with staples, nails or screws. Although a moisture barrier, such as building paper, can be placed between the lath and the sheathing, the moisture barrier must be penetrated by fasteners to secure the lath. This penetration creates holes which diminish the waterproofing features of the moisture barrier. When fasteners are driven into the sheathing, not only is the moisture barrier penetrated by the fastener, but often times the moisture barrier is torn by the lath, creating more possible water intrusion. Screw that press metal lath tear and cut the moisture barrier as they press the metal lath into the moisture barrier and sheathing. Since plaster is water absorbent, it can transmit water to more expensive and structurally important components of the building, such as the sheathing or the framing.
Lath furring strips are one way to reduce the number of penetrations into the moisture barrier because the lath is attached and secured to a furring strip, and not the sheathing or framing directly. An example of a lath furring strip is disclosed in U.S. Pat. No. 1,405,579 to Graham. This patent discloses placing a metal lath on a furring strip, which provides permanent spaces between the lath and the framing, which permits the ready application and attachment of continuous mesh reinforcements on a vertical stud. By using lath furring strips, fewer fasteners are needed to attach the furring strip to the sheathing, thus fewer penetrations are made into the moisture barrier. Furring strips have the added function of creating an air space between the sheathing and the lath, which serves the purpose of allowing the finishing material to key better, and creates insulation.
However, there are still problems with current lath furring strips. Although the use of furring strips reduces the number of holes in the moisture barrier compared to securing the lath to moisture barrier directly, water can still seep into the sheathing and framing via the holes that were created by the furring strip fasteners. A problem with adding additional waterproofing layers to the furring strip is that any additional waterproofing on the furring strip would increase the profile height of the lath furring strip. For proper plastering of walls, the plaster thickness is commonly ⅞ of an inch, and the total height from the bottom of the furring strip cannot exceed ⅜ of an inch. However, one drawback of using a lath furring strip with a profile of less than ⅜ of an inch is that it may reduce the attachment strength on the furring strip where the lath is secured. This is due to the fact that an attachment hole, where a wire tie or clamp secures the lath to the furring strip, is situated on the mounting leg of a lath furring strip. The mounting leg is what gives most of the height to the lath furring strip. The attachment hole cannot be too large because the larger the attachment hole, the less metal there is between the outer edge of the attachment hole and the outer edge of the mounting leg. The less metal there is on this mounting leg, the more easily the lath can break off of the furring strip due to the small amount of metal holding the tie, lath, and mounting leg together. Although one might consider reducing the side of the attachment hole on the mounting leg, it takes skill insert wire ties through a lath and attachment hole, and reducing the size of the hole to leave more metal in between the attachment hole and the edge of the mounting leg would make it much more difficult for the practitioner to secure the lath to the mounting leg.
Therefore, there is a need for lath furring strips with properties that increase waterproofing without increasing the profile of the plaster thickness beyond ⅞ of an inch, and maintain mounting leg strength at the attachment site of the lath.